Many nuclear reactors incorporate large assemblies of enclosing graphite blocks. The load-deflection relationship and seismic response of these blocks are of great importance, and are believed to be partially determined by the surface roughness effects at the interface between blocks. Payne [1] has attempted to calculate the ‘effective’ modulus of a graphite core structure to include the effect of contact between the individual bricks. He noted that if the brick faces become curved through irradiation, the inter-brick load will be unevenly distributed across the interface.